Characterization of Natural Rubber End Groups Using High‐Sensitivity NMR

The chemical structures of natural rubber (NR) end groups are investigated by combining chemical treatments and sensitivity‐enhanced modern nuclear magnetic resonance (NMR) spectroscopy instruments equipped with a cryoprobe. The obtained 1H NMR spectrum of the α‐end has improved signal intensity than that obtained with conventional instruments, as well as clearer splitting patterns due to the higher resolution given by the higher magnetic field. Through the 1H/13C 2D NMR experiments and the 1D NMR spectra of the model compounds, four types of α‐end structures are suggested. Two structures among them are considered related to those of mushroom‐derived NR found in the literature, whereas the others are not recognized to date. Solid‐state 31P cross‐polarization/magic angle spinning (CP/MAS) NMR is also carried out to detect the phosphate group around the terminal.